Information technology systems, including storage systems, may need protection from site disasters or outages, where outages may be planned or unplanned. Furthermore, information technology systems may require features for data migration, data backup, or data duplication. Implementations for disaster or outage recovery, data migration, data backup, and data duplication may include mirroring or copying of data in storage systems. Such mirroring or copying of data may involve interactions among hosts, storage systems and connecting networking components of the information technology system.
An enterprise storage server (ESS), such as the IBM* TotalStorage Enterprise Storage Server*, may be a disk storage server that includes one or more processors coupled to storage devices, including high capacity scalable storage devices, Redundant Array of Independent Disks (RAID), etc. The enterprise storage servers are connected to a network and include features for copying data in storage systems.
Peer-to-Peer Remote Copy (PPRC) is an ESS function that allows the shadowing of application system data from a first site to a second site. The first site may be referred to as an application site, a local site, or a primary site. The second site may be referred to as a recovery site, a remote site or a secondary site. The logical volumes that hold the data in the ESS at the local site are called local volumes, and the corresponding logical volumes that hold the mirrored data at the remote site are called remote volumes. High speed links, such as ESCON links may connect the local and remote ESS systems.
ESS currently supports a host reading directly from a secondary PPRC device. In addition, a peer-to-peer remote copy over fibre channel protocol (PPRC/FCP) relationship is typically established from a primary storage device to a secondary storage device in a PPRC operating environment. Thus, both the host and the PPRC/FCP primary may have concurrent access to the PPRC/FCP secondary device. In this case, the secondary is a target device for both the primary and an independent Host System.
The contemporaneous access of the host and PPRC primary to the secondary device can give rise to two types of problems. First, commands from the host to the PPRC secondary device can cause error conditions on the PPRC secondary device which, under small computer systems interface (SCSI) protocol, would disrupt the PPRC/FCP relationship between the primary and the secondary. For example, the host may issue a command such as a write that is not supported, an illegal request or invalid command to the PPRC/FCP secondary device. This would result in the command being check conditioned and a contingent allegiance or autocontingent allegiance (CAC/ACA) condition on the secondary PPRC device. Such a condition can inhibit the PPRC/FCP writes from the primary and result in the PPRC pairs suspending and any pending remote copies not completing. Similarly, errors encountered on the PPRC/FCP secondary device, due to the implementation of PPRC/FCP primary commands under SCSI protocol, can be disruptive to host access to the secondary PPRC/FCP device.
These problems cannot effectively be solved using SCSI protocol error handling on the secondary/target device. The host and the PPRC primary are two independent entities attempting to access the same target device. The host and the primary have no direct knowledge of the other's attempt to access the secondary. In the event of a command error on the secondary device under SCSI protocol error handling, both the PPRC primary and the host would be affected by the error and independently attempt error recovery without knowledge or coordination of the other device's error recovery attempts. This uncoordinated error handling can cause further error conditions or disruption of PPRC/FCP secondary access from both the primary and the host. Therefore, a need exists in the art for a method and apparatus to assure concurrent PPRC/FCP primary and host access to a secondary PPRC/FCP device through independent error management.
The present invention is directed to overcoming one or more of the problems discussed above.